Effect of chloride on Ca2+ release from the sarcoplasmic reticulum of mechanically skinned skeletal muscle fibres.
The effect of intracellular Cl- on Ca2+ release in mechanically skinned fibres of rat extensor digitorum longus (EDL) and toad iliofibularis muscles was examined under physiological conditions of myoplasmic [Mg2+] and [ATP] and sarcoplasmic reticulum (SR) Ca2+ loading. Both in rat and toad fibres, the presence of 20 mM Cl- in the myoplasm increased Ca2+ leakage from the SR at pCa (i.e. -log10 [Ca2+]) 6.7, but not at pCa 8. Ca2+ uptake was not significantly affected by the presence of Cl-. This Ca2+-dependent effect of Cl- on Ca2+ leakage was most likely due to a direct action on the ryanodine receptor/Ca2+ release channel, and could influence channel sensitivity and the resting [Ca2+] in muscle fibres in vivo. In contrast to this effect, acute addition of 20 mM Cl- to the myoplasm caused a 40-50% reduction in Ca2+ release in response to a low caffeine concentration both in toad and rat fibres. One possible explanation for this latter effect is that the addition of Cl- induces a potential across the SR (lumen negative) which might reduce Ca2+ release via several different mechanisms.
Coonan
J R
JR
School of Zoology, La Trobe University, Bundoora,Victoria, 3083, Australia.
Lamb
G D
GD
D000818:Animals; D002024:Bufo marinus; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002712:Chlorides / Q000494:pharmacology*; D004594:Electrophysiology; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects; D018485:Muscle Fibers, Skeletal / Q000187:drug effects* / Q000378:metabolism; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D019837:Ryanodine Receptor Calcium Release Channel / Q000502:physiology; D012519:Sarcoplasmic Reticulum / Q000187:drug effects* / Q000378:metabolism; D013314:Stress, Mechanical
D002712:Chlorides; D019837:Ryanodine Receptor Calcium Release Channel; D002110:Caffeine; D002118:Calcium